Numerous US and international agencies have identified environmental and policy interventions as the most promising strategies for improving physical activity (PA), eating, and obesity. The evidence base on environmental and policy factors is deficient in 3 important ways this proposal will address. First, although the association between built environments and PA is widely accepted by authoritative groups like the CDC's Community Guide, accurate estimates of the strength of associations are not available because virtually all studies have limited environmental variability. If underestimated associations make it less likely decision makers pursue built environment changes, then public health suffers. Second, several studies document associations between the built environment and weight outcomes, but confirmatory studies are needed, especially those conducted in diverse environments. Third, measures are insufficiently detailed to give guidance about specific attributes of the built environment most likely to be effective interventions. To accurately assess the strength of association of the built environment with PA and weight status, greater environmental variability is required than any one country can provide. Thus, we propose a collaborative international study that uses a common design and measurement protocol to produce more accurate effect size estimates. Because US-only studies are expected to underestimate effect size, this international study will provide additional information to US decision makers. The International Physical activity and the Environment Network (IPEN) is led by investigators in the US, Australia and Belgium who have demonstrated common methods can be employed across countries. IPEN builds on completed studies in the US and Australia. Six countries were selected to collect new data based on the strength of investigators, preliminary studies, and in some cases, existing partial funding. For primary aims PA will be assessed by the validated long IPAQ survey, and built environment will be assessed by a validated built environment survey in all countries (approx N=9981). Analyses will examine how specific environmental attributes are related to PA domains, leisure and transport. Most countries also will have objective measures: accelerometry for PA; Geographic Information System data for environmental attributes. Thus, subsets of countries will be used to achieve secondary aims (range of N's from 5552 to 8781). All countries will select neighborhoods that vary on walkability and recruit a minimum of 500 adults aged 20-65. Data will be entered via the web to a central server, and adherence to all protocols and data quality will be monitored. Analyses will account for multi-level data. Team members are experienced in all aspects and have conducted 3 international PA studies that show the feasibility of IPEN.